Solving the mystery of nearly 3,000 birds deaths over Lake Michigan.

Understanding the circumstances that led to the deaths of nearly 3,000 birds along the shores of Lake Michigan is actually a cold case. The deaths occurred 18 years ago, in May 1996. The National Oceanic and Atmospheric Administration (NOAA) maintains numerous weather archives, some going back more than a century. Drawing on archived data from weather stations, open water weather buoys, and weather radar data, we were able to reconstruct the likely sequence of events that led to this mortality.

Weather radar shows migrating birds encountering severe weather over the southern end of Lake Michigan. On the left, a strong band of precipitation (red) which likely included hail moved over Lake Michigan as birds (much of the blue) were migrating in the same area. The right shows a vertical cross-section of the radar data where the birds occupy the very lowest portions of the atmosphere. The precipitation forms a towering structure 12 km (>39,000 feet) high. This encounter, together with another several days later, is thought to be responsible for the death of nearly 3,000 migrating birds (Diehl et al. 2014).